Grazing in grassland ecosystems affects plant growth by removing biomass and depositing excretal nutrients. However, grazing is not uniformly distributed in space. The spatial pattern of defoliation and excretion depo...Grazing in grassland ecosystems affects plant growth by removing biomass and depositing excretal nutrients. However, grazing is not uniformly distributed in space. The spatial pattern of defoliation and excretion deposition by herbivores across vegetation mosaics has been frequently discussed, but rarely spatially quantified. A 60-day field experiment in a native semiarid grassland community was conducted to examine the responses of plant growth to simulated grazing pattern and varying nitrogen levels.Plants were subjected to five defoliation treatments determined by circularly clipped patches of different size (0, 10, 20, 40, 80cm in radius), and four nitrogen supply levels in soils (0, 5, 10, 20g N/m^2). It was detected that defoliation had reduced primary productivity by 41.5% whereas fertilization had increased it by 57.8%. The negative effect of defoliation was greater in the smallest, fertilized patches. N addition had been found to have altered the effect of defoliation, as plants growing at higher nitrogen levels were more negatively affected by defoliation than plants with no supplementary application of nitrogen. These results indicated that the magnitude of defoliation response for an individual plant was modulated by not only defoliation itself, but also other factors, such as nutrient availability, The increase in the ratio of live to dead plant parts suggested that urine deposition delayed the senescence of plants. The results also showed that (1) the effect of defoliation on primary productivity was affected by the patch size, and (2) nitrogen addition (simulated urine deposition) could increase primary productivity and affect the response to defoliation more obviously in the smaller patches than in the larger ones.展开更多
Poor, delayed and ununiform budbreak is a major problem for peaches in greenhouse. To clarify the mechanism of breaking bud dormancy in nectarines, the effect of temperature and three dormancy-breaking agents on metab...Poor, delayed and ununiform budbreak is a major problem for peaches in greenhouse. To clarify the mechanism of breaking bud dormancy in nectarines, the effect of temperature and three dormancy-breaking agents on metabolic changes during dormancy release in two-year old NJ72 nectarine (Prunus persica L. Batch) was investigated. The result showed temperature and chemicals affected the budbreak and the metabolism of NJ72 nectarine during dormancy. Endogeneous peroxide content in buds increased soon after low temperature treatment. Meanwhile, catalase activity was also shown to increase significantly at low temperature treatment, coincided with increase of the activity of peroxidase and superoxide dismutase. The rate of respiration in flower buds increased at low temperature during dormancy. The rate of the pentose phosphate pathway increased, while the rate of the Embden-Meyerhof pathway decreased and the rate of tricarboxlic acid cycle changed little. Glucose 6-phosphate dehydrogenase activity increased at low temperature during dormancy. At the same time we found an accumulation of peroxide after treatment with dormancy-breaking chemicals. In flower buds treated with dormancy-breaking agents, thiourea, KNO3 and NH4NO3, catalase activity was inhibited soon after treatment, whereas peroxidase activity increased, and the changes of superoxide dismutase remained little. In this study, it was found that the rates of respiration in flower buds increased by chemicals sprays during dormancy. The activity of glucose 6-phosphate dehydrogenase, the key enzyme in the pentose phosphate pathway (PPP), increased by spraying with dormancy-breaking agents, concomitantly with the activation of the pentose phosphate pathway.展开更多
In a series of laboratory incubations using soils of two contrasting sitesfrom a temperate marsh on the Qinghai-Tibet Plateau, potential methane (CH_4) oxidation rates weremeasured to study the effects of inorganic N ...In a series of laboratory incubations using soils of two contrasting sitesfrom a temperate marsh on the Qinghai-Tibet Plateau, potential methane (CH_4) oxidation rates weremeasured to study the effects of inorganic N inputs on CH_4 oxidation. For adrained site, subsurfacepeat (5--15 cm) at an initial 20 mu L CH_4 L^(-1) showed a significantly different (P < 0.05) CH_4oxidation rate compared to other soil depths, with a maximal rate of 20.9 ng CH_4 gDW (dryweight)^(-1) h^(-1); the underlying mineral soil layers (15--30 and 30--50 cm) also had a strongCH_4 oxidation capacity at about an initial 2 000 mu L CH_4 L^(-1). With a waterlogged site, theCH_4 oxidation rate in an aerobic incubation was significantly greater (P < 0 05) in the surfacesoil layer (0--5 cm) compared to the 15--30 and 30--50 cm depths. There was generally no or a veryweak effect from addition of NO_3^- on CH_4 oxidation. In marked contrast, NH_4^+ salts, such as(NH_4)_2SO_4, NH_4Cl and NH_4NO_3, exhibited strong inhibitions, which varied as a function of theadded salts and the initial CH_4 level Increasing NH_4^+ usually resulted in greater inhibition andincreasing initial CH_4 concentrations resulted in less NH_4^+ inhibition on CH4 oxidation innatural high-altitude, low-latitude wetlands could be as important as has been reported foragricultural and forest soils. The NH_4^+ effects on the CH_4 oxidation rate need to be furtherinvestigated in a wide range of natural wetland soil types.展开更多
文摘Grazing in grassland ecosystems affects plant growth by removing biomass and depositing excretal nutrients. However, grazing is not uniformly distributed in space. The spatial pattern of defoliation and excretion deposition by herbivores across vegetation mosaics has been frequently discussed, but rarely spatially quantified. A 60-day field experiment in a native semiarid grassland community was conducted to examine the responses of plant growth to simulated grazing pattern and varying nitrogen levels.Plants were subjected to five defoliation treatments determined by circularly clipped patches of different size (0, 10, 20, 40, 80cm in radius), and four nitrogen supply levels in soils (0, 5, 10, 20g N/m^2). It was detected that defoliation had reduced primary productivity by 41.5% whereas fertilization had increased it by 57.8%. The negative effect of defoliation was greater in the smallest, fertilized patches. N addition had been found to have altered the effect of defoliation, as plants growing at higher nitrogen levels were more negatively affected by defoliation than plants with no supplementary application of nitrogen. These results indicated that the magnitude of defoliation response for an individual plant was modulated by not only defoliation itself, but also other factors, such as nutrient availability, The increase in the ratio of live to dead plant parts suggested that urine deposition delayed the senescence of plants. The results also showed that (1) the effect of defoliation on primary productivity was affected by the patch size, and (2) nitrogen addition (simulated urine deposition) could increase primary productivity and affect the response to defoliation more obviously in the smaller patches than in the larger ones.
基金supported by the Major Research Project of the Chinese Academy of Sciences(KSCX1-08-03)the State Key Basic Research and Development Plan of China(G2000018603)the Foundation of Educational Committee of Shandong Province(32179).
文摘Poor, delayed and ununiform budbreak is a major problem for peaches in greenhouse. To clarify the mechanism of breaking bud dormancy in nectarines, the effect of temperature and three dormancy-breaking agents on metabolic changes during dormancy release in two-year old NJ72 nectarine (Prunus persica L. Batch) was investigated. The result showed temperature and chemicals affected the budbreak and the metabolism of NJ72 nectarine during dormancy. Endogeneous peroxide content in buds increased soon after low temperature treatment. Meanwhile, catalase activity was also shown to increase significantly at low temperature treatment, coincided with increase of the activity of peroxidase and superoxide dismutase. The rate of respiration in flower buds increased at low temperature during dormancy. The rate of the pentose phosphate pathway increased, while the rate of the Embden-Meyerhof pathway decreased and the rate of tricarboxlic acid cycle changed little. Glucose 6-phosphate dehydrogenase activity increased at low temperature during dormancy. At the same time we found an accumulation of peroxide after treatment with dormancy-breaking chemicals. In flower buds treated with dormancy-breaking agents, thiourea, KNO3 and NH4NO3, catalase activity was inhibited soon after treatment, whereas peroxidase activity increased, and the changes of superoxide dismutase remained little. In this study, it was found that the rates of respiration in flower buds increased by chemicals sprays during dormancy. The activity of glucose 6-phosphate dehydrogenase, the key enzyme in the pentose phosphate pathway (PPP), increased by spraying with dormancy-breaking agents, concomitantly with the activation of the pentose phosphate pathway.
基金Project supported by the Knowledge Innovation Project in Resource and Environment Fields, Chinese Academy of Sciences (No. KZCX3-SW-128), the Open Foundation of the State Key Laboratory of Gas Geochemistry (SJJ-01-07), and the National Key Basic Research
文摘In a series of laboratory incubations using soils of two contrasting sitesfrom a temperate marsh on the Qinghai-Tibet Plateau, potential methane (CH_4) oxidation rates weremeasured to study the effects of inorganic N inputs on CH_4 oxidation. For adrained site, subsurfacepeat (5--15 cm) at an initial 20 mu L CH_4 L^(-1) showed a significantly different (P < 0.05) CH_4oxidation rate compared to other soil depths, with a maximal rate of 20.9 ng CH_4 gDW (dryweight)^(-1) h^(-1); the underlying mineral soil layers (15--30 and 30--50 cm) also had a strongCH_4 oxidation capacity at about an initial 2 000 mu L CH_4 L^(-1). With a waterlogged site, theCH_4 oxidation rate in an aerobic incubation was significantly greater (P < 0 05) in the surfacesoil layer (0--5 cm) compared to the 15--30 and 30--50 cm depths. There was generally no or a veryweak effect from addition of NO_3^- on CH_4 oxidation. In marked contrast, NH_4^+ salts, such as(NH_4)_2SO_4, NH_4Cl and NH_4NO_3, exhibited strong inhibitions, which varied as a function of theadded salts and the initial CH_4 level Increasing NH_4^+ usually resulted in greater inhibition andincreasing initial CH_4 concentrations resulted in less NH_4^+ inhibition on CH4 oxidation innatural high-altitude, low-latitude wetlands could be as important as has been reported foragricultural and forest soils. The NH_4^+ effects on the CH_4 oxidation rate need to be furtherinvestigated in a wide range of natural wetland soil types.
